Sequence control of color change

ABSTRACT

A pneumatically controlled color change system for use with automatic multi-color paint spray apparatus and the like wherein an entirely pneumatically controlled system employing a pneumatic timer including pneumatic sequence valves controls a quick-color change system in which a plurality of colors of paint are connected to various inputs of a manifold, each through a check valve which isolates each of the manifold ports from each other and in which a source of solvent is connected to another input of the manifold. An exceedingly high-speed system is provided in which a metered charge of solvent only partially filling the system is injected through the manifold and forced through the system with the new color to be selected, thereby purging the system of the old color. High-speed valve timing is provided in the order of magnitude of 1 second per valve of the sequence.

United States Patent Scarbrough et a].

[451 June 27, 1972 SEQUENCE CONTROL OF COLOR CHANGE Appl. No.: 69,662

3,572,366 3/1971 Wiggins ..239/112 Primary Examiner-Lloyd L. KingAttorney- Wood, Herron & Evans [5 7] ABSTRACT A pneumatically controlledcolor change system for use with automatic multi-color paint sprayapparatus and the like wherein an entirely pneumatically controlledsystem employing a pneumatic timer including pneumatic sequence valvescontrols a quick-color change system in which a plurality of [52] US. Cl..239/70, 239/112 [51] Int. Cl ..A01g 27/00 colors of palm are connectedp Inputs of a mamfold 58] Field Search 239/61 62 70 I24 I25 each througha check valve which isolates each of the 6 manifold ports from eachother and in which a source of solvent is connected to another input ofthe manifold. An exceedingly high-speed system is provided in which ametered [56] References Cited char e of solvent only partially fillinthe system is injected 8 8 UNITED STATES PATENTS through the manifoldand forced through the system with the new color to be selected, therebypurging the system of the old 3,348,774 10/1967 Wiggins ..239/70 colorHigh speed valve timing is provided in the order ofmag 5 nitude of 1second per valve of the sequence. 0p ms.. 3,450,092 6/1969 Kock ..239/7024 Claims, 9 Drawing Figures a M Q1 I h 5 2c cam/ 1:7:

m mclra? SEQUENCE CONTROL OF COLOR CHANGE The present invention relatesto a quick-change system for use with a single gun operable toselectively discharge different coating liquids, such as paints ofdifferent color, or varnishes, waxes, protective coating materials orother surface treating liquids upon a substrate. More particularly, thepresent invention relates to a quick-color change system in which thepaint is sprayed or discharged from the nozzle, and deposited upon asubstrate or object to be painted. The present invention is specificallydirected to such a quickchange spray system for changing from one liquidto another without the previously used old liquid contaminating the newliquid when it is sprayed.

The increased use of automated painting and coating apparatus such as inassembly lines on automobile plants, or a series of objects to bepainted or otherwise coated pass a paint station, and in which theseobjects typically require the applications of different coatings andcolors, have resulted in an increased demand for multiple color paintspray systems. While systems have been proposed utilizing a separateapparatus having a separate nozzle for each of the colors or coatingliquids to be sprayed, such systems are cumbersome and unduly expensive.The utility of systems wherein a single apparatus having a singledischarge nozzle, or single set of nozzles as the requirement may be,for spraying the plurality of coating liquids one at a time, has residedin the ability of the color change system to change from one color toanother quickly with a minimum waste of paint and solvent. Typically,these systems employ a manifold to which the plurality of coatingliquids is connected and through which one of the plurality of coatingliquids is selectively connected to the coating apparatus. When changingfrom one coating liquid to another, it is necessary to purge themanifold, the feed line connecting the manifold to the apparatus, andthe apparatus itself of the old coating liquid prior to the injection ofa new coating liquid. Commonly, the solvent material is injected intothe system to force the old liquid out of the system through a dumpvalve and to flush the system of the old coating liquid. A common methodemployed by the prior art systems have been to manually cause thesolvent to be injected into the system and to visually observe a cleansolvent being exhausted through the dump valve. Then, either air isinjected into the system to purge the system of the solvent, or the newcoating liquid is in jected to push ahead of it the solvent from thesystem. These systems of the prior art have consumed much valuable timeand wasted a great deal of paint and solvent in changing color in thismanner. Indeed, in automotive paint lines, where each of the objects isto be painted a different color, the waste of time and paint can be amajor cost factor.

Furthermore, automated systems of the prior art rely prin cipally uponvalves controlled by electrical solenoids to automatically sequence achange cycle. Since such systems are almost always used in a highlyexplosive atmosphere, these electrical control systems have been encasedin sealed, armored explosion-proof cabinets. In many cases, the cabinetshave been installed at greater cost than the systems themselves. Anotherdisadvantage of such explosion-proofing has been the requirement thatthe entire system be shut down whenever any maintenance is required uponthe system, even minor maintenance, for the explosion-proof cabinet hadto be opened to allow such maintenance to proceed.

Accordingly, it has been the principal object of the present inventionto provide an explosion-hazard-free control system which uses entirelyfluid-controlled valves and fluid-controlled timing circuits to operatethe valves. Another object of the present invention has been to providea change system which operates faster than comparable systems of theprior art, typically in the order of l to 5 seconds in situations whereprior art systems have required 25 seconds and above; and generally notmore than 20 seconds for a complete change cycle in some of the morespecial application systems which utilize high viscosity liquids, verylong lines or lower pressure, in which systems the prior art deviceshave typically required a minute or longer for such a change.

Accordingly, the present invention is predicated in part upon theconcept of providing an all-fluid-controlled valve system which iscontrolled entirely through the use of a fluid control circuit whichincludes a fluid-operated timing circuit for controlling the sequencingof the valves during a liquid change cycle. More particularly, thepresent invention provides a fluid control system employing variabletime delay pneumatic sequence valves which deliver control pressure froma variable control pressure source to operate the liquid flow controlvalves in a programmed color change sequence.

The present invention is also predicated in part upon the concept ofinjecting a metered slug of solvent into the lines of the system, theslug being only long enough to purge the system of the old color, andthen forcing the slug through the system with the new coating liquid tobe applied. Further more, the present invention employs valve openingtimes in order of magnitude of I second each.

Furthermore, the present invention employs a novel manifold arrangementwherein each of the input ports of the manifold includes a double-checkvalve arrangement. More particularly, one of the check valves of thisdouble-check valve arrangement is the remote control valve whichconnects the particular liquid to the system, and the other is a checkvalve which isolates from the manifold all but a small region in thepath of the solvent passing through the manifold and thereby presents anarea easily flushed of the solvent. The advantage of this manifoldarrangement is that it is easily and quickly cleaned or flushed of oneliquid preparatory to the introduction of another.

The primary advantages of the present invention reside in the provisionfor an automatic, quick-change system which is completely safe for usein an explosive environment without the need for expensiveexplosion-proof cabinets and the impairment for servicing duringoperation which they entail. An additional important advantage is in theprovision for highspeed paint change system, wherein the complete changefrom one coating liquid to another in an airless system takes the timeof typically 4 to 10 seconds. A further advantage resides in thevariable timer of such a system so that the times of the various stepsof the cycle can be varied either independently or collectively toaccount for different types and viscosities of coating liquids. Anotheradvantage is that it substantially reduces any wasted paint and solventwhich results from the use of this liquid change apparatus.

Other advantages of the present invention which will be more readilyapparent from the detailed description of the present invention residein the provisions for positive interlocking sequencing of thequick-change system, manual emergency shut-off of the system, a systemwhich is essentially the same regardless of the number of colors ordifferent coating liquids to be used, and a system which can beconstructed virtually from standard components.

Other objects and advantages of the present invention will be morereadily apparent from the following detailed description of the drawingsillustrating one preferred form of a quick change system according tothe present invention in which:

FIG. 1 is a fluid control diagram of a quick change system according tothe present invention;

FIG. 2 is a timing diagram of the operation of the system of FIG. 1;

FIGS. 3-6 are diagrams of the system of FIG. 1 illustrating the statesof the different coating liquids and solvent at the different timesillustrated at 1,-1, in FIG. 2;

FIG. 7 is a partial cut-away view of the coating liquid and solventdistribution manifold;

FIG. 8 is an enlarged cross-sectional view of the double check valve atan input port of the manifold of FIG. 7; and,

FIG. 9 is a cross-sectional view of a coating liquid discharge gun.

Referring to the system diagram of FIG. 1, a quick change systemaccording to one of the principles of the present invention includes apaint discharge gun 10 which is of the circulating type, that is, itincludes three ports, including an input port ll through which paintenters the gun, and outlet port 12 through which paint exits thatparticular gun, and a nozzle 13 through which paint or other coatingmaterial is sprayed upon a substrate to be coated.

The gun includes an internal passage 14 which communicates with theinput and exhaust ports directly, and also communicates with the nozzle13 through a trigger valve 15. The trigger valve 15 is typicallylever-operated when the gun is a hand-held type. In the embodimentshown, however, the gun 15 is remotely controlled through theapplication of control pressure to the pilot port [6. This form ispreferred when the gun is either fixedly or movably mounted upon asupport such as might be found adjacent a paint line in an automobileassembly plant. An outlet line 17 is connected through a dump valve 18to a return line 22 which communicates with the exhaust port 12 of thegun 10. The dump valve operates in response to control pressure at thepilot port 19 to open the exhaust line 17 to allow paint to be purgedfrom the gun l and drained into a scrap drum 20. The dump valve 18 isnormally closed to block the exhaust line 17 in the absence of controlpressure at the pilot port 19.

Paint is supplied to the gun through a feed line 21 which is connectedto the input port 11 of the gun 10. Whereas the gun It) is preferably ofthe circulating type as herein described in order that the maximumamount of trapped old paint can be purged from the system through theoutlet port rather than the nozzle, it is within certain of the broaderconcepts of the present invention to operate without such a circulatinggun. In such cases, it is preferable that a T be incorporated andconnected to the feed line at some point prior to the input 11 of thegun It] and preferably as close thereto as possible. A return line,external of the gun, is then connected between the T and the dump valve.

The selected color of paint or coating liquid is supplied to the gunthrough a manifold 25. The manifold has an output port 26 which connectsto the feed line 2], and a plurality of input ports 27 each connectingthrough a shut-off valve 28 to any one of a plurality of lines 29 whichare connected to various sources of coating liquid.

The manifold 25 has therein an elongated passage or through-port 30(FIGS. 3-7) which communicates each input port 27 with the output port26. The manifold also includes an input port 31 which is connectedthrough a cut-off valve 32 to line 33 which is connected to a source ofpressurized solvent. The input port 31 communicates with the passage 30at a point which is the most remote from the output 26 of the manifold.Thus the input ports 27 communicate with the passage 30 at pointsintermediate the solvent input port 31 and the output port 26 so thatthe solvent when passed by valve 32, can most effectively flush themanifold 30 clear of the old coating liquid of the previous applicationprior to subsequent application ofa difl'erent coating liquid.

The pressure of the sources of coating liquid connected to the sourcelines 29 is typically 200 to L000 psi for spray systems of the airlesstype, and is typically 3-75 psi for systems of the air spray type. Anairless system is one in which paint is sprayed at high pressure andatomized solely by forcing the high pressure liquid through the nozzleof a paint spray gun. In

an air system, the liquid is injected as an extruded stream at lowpressure into a stream of high pressure air which causes it to atomize.The present invention can operate with either system, but in thepreferred embodiment shown, the airless system is employed with sourcepressures of approximately 500 psi.

Each of the coating liquid valve 28 and the solvent valve 32 arenormally closed. The coating liquid valves 28 are opened in response tocontrol pressure at their pilot ports 34, and the solvent valve 32 isopened in response to control pressure at its pilot port 38. Each of thepilot ports 34 of the liquid coating valves 28 connect to the outputports 36 of a rotary selector valve 37. The pilot port 38 of solventvalve 32 is connected to an output 39 of the selector switch 37 to allowfor selection of the solvent as one of the coating liquids. As isdescribed in more detail below, the solvent valve 32, is however, alsooperated under the control of a timing circuit which applies controlpressure through a control line 41. The selector switch output 39 andthe line 41 are alternately connected to the pilot port 38 of thesolvent valve 32 through the shuttle valve 42.

The selector 37 also has an input port 44 which is selectivelyconnectable to any one of the output ports 36 or 39 through the manuallymovable spool 45 which is controlled either by the dial 46 orautomatically through a programmer (not shown) to select new coatingmaterials. The ports 36 which are not connected to the input port 44 arenormally connected to an exhaust port 47 at atmospheric pressure. Afluid pressure responsive selector lock 48 is provided to lock the spool45 of the selector valve 37 and thereby prevent a change in selectionwhile an automatic change cycle is in progress.

The automatic control and timing circuit is entirely apneumatically-controlled system in which the source of control pressureis supplied from an air pressure source 50. The control pressure isnormally maintained at approximately 40-70 psi. The air pressure source50 connects through a filter 51 and a variable air pressure regulator 52to the input port 53 of a manually actuatable four-way valve 54. Thevalve 54 is the main control valve which provides for the manualstarting and stopping of the color change cycle. The valve 54, however,couid also be automatically controlled by a programmer, for example, ifthe present invention were used as part of a completely automatedpainting process. The valve 54 has an exhaust or drain port 55 and apair of output ports 56 and 57. When the valve is in its de-actuatedcondition, the port 57 is normally connected to the pressure input port53 to communicate a ready signal to a pressure responsive indicator 58,while the output port 56 is connected to exhaust port 55. This removespressure from the control circuit, and, because all valves are normallyclosed, the change system is at this time disabled. The valve 54 has amanual override to utilize this feature for emergency cut off of thesystem. When the valve 53 is actuated the output port 56 communicateswith the in put port 53 thereby opening the pressure path through thevalve 54 to a line 61 connected to the output port 56 to initiate thechange cycle. Line 61 is connected through a line 62 to the pilot port49 of the pneumatically controlled selector lock 48 to energize the lock48 and lock the selector switch 37. The line 61 is also connectedthrough line 63 to the pneumatic timing circuit illustrated generally at65.

The timing circuit 65 is an entirely pneumatically controlled timingcircuit for generating a series of timed-delayed control signals. Thetiming circuit 65 employs sequence valves or series-connectedtimed-delay valves which actuate at some delayed time after pressure isapplied to their input terminals. The specific circuit illustratedemploys three such valves, 71, 72, and 73, however, more or less thanthree could be employed as will be explained more fully below. Each ofthe valves 71 and 73 are substantially identical and will be explainedhere by reference to valve 717 The first timing valve 71 includes afour-way valve 77, having an input port78 and a pair of ports 79 and 80.The output port 79 is a normal through-port of the valve while thesecond output port 80 is normally connected to an exhaust port 81. Whenthe valve is actuated, the output ports are reverse connected and thefirst output 79 is connected to the exhaust port 81 while the secondoutput port 80 is connected to the input port 78. The valve 77 actuatesin response to control pressure of a certain predetermined level at apilot port 82. The pilot port 82 is connected through a variablerestriction valve 83 to the input ports 78. The restriction valve 83serves to impede the flow to the pilot port 82 thereby delaying the timeat which the predetermined pressure required to actuate the valve isattained at the pilot port 82. This time delay can be variablycontrolled by the setting of the valve 83. It should also be noted, thatthe actual time delay is also dependent upon the setting of the pressureregulator 52. Setting the valve 83 varies the delay time of valve 81independently of other valves in the circuit, while setting theregulator 52 varies the response of all valves of the circuit byapproximately the same factor. A check valve 84 is provided to quicklyrelease the pressure on the pilot port 82 when the pressure on the inputport 78 is removed. Thus, when pressure is applied to the input port 78by the opening of the main valve 54, a control pressure signal ispresent at the output 79. After a certain time delay determined by thesetting of the restriction valve 83, the four-way valve 77 is actuatedand pressure on line 79 is removed and applied to port 80.

In like manner valve 72 has an input port 87, first output port 88 and asecond output port 89. The input 87 is connected to the output port 80of the valve 71. The valve 72 includes a variable restriction valve 91,which determines the time delay constant of the valve 72. Thus, when thevalve 71 is actuated, a control pressure signal appears at port 88, andafter a predetermined time delay determined by the setting of the valve91, the signal is removed from the port 88 and transferred to the port89.

Similarly, the valve 73 includes an input port 92 connected to thesecond output port 89 of the valve 72, and a first output port 93 andthe second output port 94. The valve 73 includes a variable restrictionvalve 95 which determines the time delay constant to the valve 73. Thus,after valve 72 is actuated, a control signal appears at port 93, andafter a time delay determined by the setting of the valve 95, the signalis removed from the port 93 and transferred to port 94. Connected toport 94 is a pressure response indicator 96 which signals the completionof a change cycle.

The output port 79 of the valve 71 is connected to line 41 and throughthe shuttle valve 42 to the pilot port 38 of the solvent valve 32, andalso through a shuttle valve 97 to the pilot port 19 of the dump valve18. The output 80 of the valve 71 is connected to the input 44 of theselector valve 37. (This is equivalent to connecting the selector input44 through a shuttle valve to ports 89 and 93 of the timer and thislatter method would be preferred if an additional step were added to thesystem.) The output 88 of the valve 72 is connected through another portof the shuttle valve 97 to the pilot port 19 of the dump valve 18. Theoutput 93 of the valve 73 is connected to a shuttle valve 98 to thepilot port 16 of the trigger valve 15 of the gun 10. Also connectedthrough the shuttle valve 98 to the pilot port 16 of the trigger valve15 is a control line 99 through which a signal is provided to operatethe paint spray gun during painting operations between change-cycles.

Briefly, the timing operation can be understood by reference to thetiming diagram of FIG. 2. Prior to a change cycle, the main valve 54 isin the closed condition and the ready indicator is ON" as illustrated bythe curve 101 on the diagram. At some time t, the main valve is opened,as illustrated by curve 102. At this time control pressure is applied toenergize the selector lock as illustrated by curve 103 and to open thesolvent and dump valves as illustrated by curves 104 and 105. Thisinitiates the time delay T of the first of the sequence valves 71 at theend of which valve 71 is actuated at a time represented by t, in FIG. 2.At time I, the solvent valve is closed and the new color valve asselected by the setting of the selector valve 37 is opened asillustrated by curve 106.

At time I, control pressure is also removed from the pilot input 19 ofthe dump valve 18, however, this pressure is reapplied through the valve72 and in practice this time is too short to result in a closing of thedump valve 18. After a time delay T, the valve 72 closes, and causes thedump valve 18 to close as shown by curve 105. This is illustrated attime t, in FIG. 2. At t, pressure is applied through the third of thetiming valves 73 to momentarily open the trigger valve for a period oftime T, after which valve 73 closes, and time 1, closing the new colorvalve, and the trigger valve, of the gun as shown by curve 106 and 107.Also at time t, the complete indicator is turned on as illustrated bycurve 108 in FIG. 2 and the selector lock 48 is de-energized asillustrated by curve 103. At this point the main valve 54 can either bemanually or automatically disengaged as the color change-cycle iscomplete.

The change-cycle can best be understood by reference to FIGS. 3 through6 which illustrate the highly efficient manner in which the lines areonly partially purged by the injection of solvent, and then finallypurged of the old coating liquid 111 through the injection of the newcoating which pushes ahead of it a metered slug of solvent which cleanthe lines of the old material. With reference back to the timing diagramof FIG. 2, FIG. 3 illustrates the system prior to a change-cycle at timer It will be seen that the passage 30 of the manifold 25, the feed line21, the pusage 14 of the gun 10 and the nozzle 13 are filled with theold coating material 111 being supplied through valve 34-B.

Prior to the color change, the selector dial 46 of the selector valve 37is set to the new paint color or coating liquid and the main valve 54 isactuated.

During this first step (FIG. 4) of the cycle, the solvent valve 32 andthe dump valve 18 are opened, and the trigger valve 15 of the gun 10 isclosed. This allows solvent to enter into the manifold passage 30 and toforce the old paint through the dump valve 18 into the scrap drum 20. Attime t. a slug of solvent 112 has entered the manifold passage 30 andproceeded partially down the length of the feed line 21 to point 113.The solvent slug 112 is not allowed to completely extend through theentire feed line 21 to purge the entire system since this is notnecessary. Instead, only a slug of sufficient length to clear thepassage 30 is employed. Typically about 2-5 feet of manifold passage andfeed line would be filled with solvent. At this point and as shown inFIG. 5, the solvent valve 32 is closed and the new liquid valve 34-E isopened. The new liquid 115 is introduced into the manifold passage 30and along the feed line 21 to advance the slug of solvent 112 as far asthe juncture of the trigger valve 15 with the passage 14 of the gun 10.At this point it is still not necessary to completely purge the oldliquid 111 from the exhaust line 17. The length of the slug 112 issufficient to completely wash the line 21 of the old liquid. FIG. 5illustrates the state of this system at time t,.

Referring to FIG. 6, the dump valve 18 is closed but the source valve34-1-2 remains open communicating the pressurized new color with thepaint lines 21. At this time the trigger valve is opened and preferablythe new paint color is fed through the nozzle, thereby discharging theold paint 111 which remains in the nozzle. In some applications,however, it may be desirable to eject a small amount of solvent throughthe nozzle to purge it of old paint. At time t. the trigger valve 15closes and the system is ready for operation with the new color 115.

Referring back to FIG. 5, it will be noted that it is possible for asmall amount of solvent to remain trapped in the manifold in the region117. This solvent, however, is normally selected such that it iscompatible with the coating and will diffuse and dissipate into the newliquid mixture without affecting the quality of the coating. As will beexplained below, the manifold of this system has the particularadvantage of minimizing the amount of this trapped solvent.

As mentioned above it is possible to operate this system with fewer ormore timing valves than the three illustrated in FIG. 1. For example,where the hand-held gun is employed, the valve 73 is not required, inthis case, the operator, merely by aiming the gun into the scrap drumand momentarily depressing a manual trigger can thereby expel the oldliquid 111 from the nozzle into the drum. In other cases, it issometimes desirable to employ more valves than three in situations wheremore steps are required. For example, when incompatible coating liquidsare to be employed in consecutive steps, it may be desirable to producea charge of air to purge the old paint from the system and through theexhaust line 17. It also may be required in such situations to employdifferent solvents and to separate the solvents by a charge of air.Occasionally, a strong solvent might be used which is incompatible withthe coating liquid. This solvent would be injected in the same mannerthrough the sequences illustrated of the FIG. 4, but then followed by acharge of air to expel the solvent through the exhaust line 17, which isthen followed by the new coating liquid.

Referring more particularly to the details of the manifold 25, this isbest illustrated by reference to FIG. 7. The manifold 25 includes ahousing I20 having the through port or central passage 30 extendingsubstantially therethrough. The output port 26 is provided in one end ofthe passage 30 and the solvent input port 31 is provided adjacent theinnermost end. Intermediate these extreme ends the plurality of inputports 27 are connected to passage 30, each connecting through one of thecoating liquid valves 28 through lines 29 to corresponding coatingliquid sources. The solvent input port 31 connects through the solventinput valve 32 to the solvent source line 33 which is connected to asolvent source. The dump valve I8 is also physically mounted on themanifold housing 120 and connects through a passage I21 therein to theexhaust line 17. The passage I2] is, however, completely isolatedhydraulically from the passage 30.

In one embodiment, each of the valves I8, 28 and the valve 32 may beidentical and hence only one valve 28 is illustrated in the cut-awayportion of the drawing (FIG. 7). However, in a preferred embodiment formany applications, the valves 28 are of the circulating type and eachwill be identical to that illustrated for the trigger valve 15 of thegun It) in FIG. 9. The dump valve 18, however, and the solvent valve 32,are usually non-circulating even in this preferred embodiment. Anexample of such a circulating type system is completely illustrated anddisclosed in US. Pat. No. 2,754,228 of Bede, issued July 10, I966. Asnoted above, the valve includes the input line 29 which communicateswith an internal passage I22. The passage 122 communicates through apneumatically controlled check valve I23 to the input 27 of themanifold. Control pressure for opening the check valve I23 is suppliedthrough the pilot port 34. The details of the source valves 28 and 32are identical to the details of the operating mechanism of the triggervalve I of the gun I0 and will be explained in more detail inconjunction with the description of the trigger valve of the FIG. 9.

The check valve 123 forms one of the check valves of a double-checkvalve assembly 125. This check valve arrangement prevents back flow ofthe coating liquid or solvent and thereby prevents contamination of oneliquid coating with another. The valve also presents a minimum washingarea for the solvent to purge of coating material. The valve 125 is moreclearly illustrated in the cross-section view of FIG. 8. The valve 125comprises a narrow throat 130 adjacent the check valve 123. A checkvalve I31 is provided in a close relation to the check valve I23 andalso adjacent the throat 130 opposite the check valve 123. The checkvalve I3] is a passive check valve operating entirely by the pressure ofthe paint from the source through the valve I23. The valve I3I includesa ball or check I32 urged by a spring 133 against the rim of the walls134 of the throat section 130. The check valve I3] presents only a smallsurface area 135 which lies directly in the path of the passage 30 andis easily washed by the solvent as it passes through the passage 30.

Referring to FIG. 9, a paint spray gun is illustrated. The gun isgenerally a recirculating airless-type having an input port I1, andoutlet port 12 and a nozzle 13. The nozzle is operated by a triggervalve in response to control pressure at the pilot port I6 to connectthe nozzle with the internal passage I4 of the gun I0. While an airlessspray nozzle I3 is illustrated, a typical use of the system of thepresent invention is contemplated to be in conjunction with anelectrostatic spray gun having a nozzle extension which will typicallyproject several times a length of the nozzle 13 as illustrated.

As it will be seen from FIG. 9, the gun 10 generally comprises atwo-piece square body 140 within which there is an axial or central bore141. This bore comprises the internal passage or fluid chamber I4adjacent the front end of the body, a smaller diameter connectingchamber 144 and a large diameter piston chamber 145. The chamber 144 isconnected to atmosphere through a bleed port 143. The rear side of thepiston chamber I45 is opened to the atmosphere through a small diametersection 146 of the bore 141 which is connected to the piston chamber I45via an intermediate diameter chamber 147. An end cap 148 is secured tothe body by bolts (not shown) and closes the fluid chamber 14. The cap148 comprises a central plate 149 from which hub sections 150, 15]extend rearwardly and forwardly, respectively. The rearward hub I50 fitswithin, and with an O-ring, seals the fluid chamber 14. The forwardlyextending hub section 151 is threaded on its exterior as indicated at154 and has an inwardly extending flange I55. An axial bore 156 extendsthrough the cap 148. It comprises a large diameter rear section 157 anda smaller diameter front section 158.

A cylindrical metal insert 159 made from a hard material, as forexample, tungsten carbide, is inserted within the small diameter section158 of the cap. This insert defines the seat of the check valve I5. Ithas a stepped axial bore which comprises a large diameter rearwardsection 160 and a small diameter passage I61 interconnected by ashoulder I62. An arcuate seat 163 is machined into the shoulder at thepoint where the shoulder I62 joins the small bore 16!. The seat isconfigurated as an annular taper so as to cooperate with a generallysemi-spherical end 165 of the check valve head 166 to form a seal.

The nozzle 13 is made of a hard material and is welded to a nozzlemounting disc 169. A retaining nut 170 is threaded onto the externallythreaded section 154 of the hub 15]. This retaining nut secures the disc169, which carries the spray nozzle 13, against the hub 151 of cap 148.

It will be seen that the check valve head I66 is controlled in itsmovement into and out of engagement with the check valve seat I63 by thepneumatic piston 185. This piston is connected to the head end of thecheck valve by a connecting rod 186. A conventional threaded couplingand lock nut I84 enable the rod 186 to be adjusted in length relative tothe head 166. A compression spring 187 normally biases the head andconnected piston rod I86 toward the nozzle to a position in which thecheck valve I5 is seated or closed. This spring I87 bears at one endagainst the nut 184 and at the opposite end against a collar 188 whichis fixedly seated in the chamber 144 of bore I41 and has a shoulder orflange I89 seated against a shoulder 190 of the bore 141. O-rings I91and I92 seal the liquid chamber 14 from the pneumatic chamber 145, andvice versa. The forward end of the piston chamber I45 is also sealedfrom the rear portion 196 by a pneumatic seal I97 located around theperiphery of the piston 185. The piston is secured onto the end of therod 186 by a pair of lock nuts I98 and 199 threaded onto the threadedinnermost end 200 of the rod 186. Air under regulated pressure, e.g.,approximately 60 psi is supplied to the inner chamber 195 of the pistonchamber 145 from the pilot port 16 via a connecting passage 210 in thebody 140 of the gun 10.

The primary advantage of this invention over quiclcchange color spraysystems now being used commercially is that it eliminates all use ofelectrical solenoid-controlled valves and control circuits and therebyavoids the hazard of an electrically initiated explosion. By eliminatingall electronic sequencing and control there is no longer any need toexplosion-proof the area in which the paint is sprayed and the gun isutilized.

Another advantage of this invention is the positive sequencing whichresults from the pneumatic sequencing control valves. In the event thatone valve stops or jams, it automatically stops the complete cycle,thereby insuring a properly sequenced cycle or none at all.

Another advantage of this invention resides in its quick cycle time andthe fact that it operates in approximately onefourth to one-tenth thecycle time of quick-change color systems now in commercial use. Becauseit is so much faster than systems in present use, it results in lesswasted paint being dumped to scrap and less solvent being utilized topurge the system during color changes.

While only a single preferred embodiment of the invention is described,those persons skilled in the art to which this invention pertains willreadily appreciate numerous changes and modifications which may be madewithout departing from the spirit of the invention. For example, it willsometimes be desired to incorporate certain of the features andadvantages derived from the fluid operated control aspects of thepresent invention while omitting the automatic sequencing feature. Insuch a case, the flow control valves can be provided with independentlyactuatable fluid control valves which may be, for example, manuallyactuatable pneumatic remote control vales connected through controllines to the pilot ports of the flow control valves mounted on themanifold or to the triggercheclt valves of the gun. Therefore, thepresent application is not intended to be limited except by the scope ofthe appended claims.

What is claimed is:

I. An automatic quick-change system for replacing an old coating liquidwith a new coating liquid in an apparatus for selectively depositing acoating liquid on a sub-strate, said system comprising:

a. a discharge gun having an input port, an exhaust port, a

passage therein communicating with said input and exhaust ports, anozzle, a check valve connected between said passage and said nozzle forconnecting said nozzle to said passage when said check valve is opened;

. an exhaust line;

. a fluid-controlled dump valve having a pilot port and connectedbetween said gun exhaust port and said exhaust line for connecting saidgun exhaust port to said exhaust line in response to control pressure atsaid dump valve pilot port;

(1. a manifold having an output port, a solvent input port, an

elongated passage therein communicating with said output port and saidsolvent port, and a plurality of coating liquid input portscommunicating with said manifold passage intermediate said output andsaid solvent input ports;

e. a feed line connected between said manifold output port and said guninput port;

f. a source of pressurized solvent;

g. a fluid-controlled solvent valve having a pilot port and connectedbetween said solvent source and said solvent input port of said manifoldfor connecting said solvent source to said manifold input port inresponse to control pressure at said solvent valve pilot port;

h. a plurality of sources of different pressurized coating liquids;

. a plurality of fluid-controlled coating liquid valves each having apilot port and each connected to a different one of said coating liquidsources and a difi'erent one at said one of said sources with said oneof said ports in response to control pressure at said coating liquidvalve pilot port;

j. a fluid control circuit including:

l a source of pressurized control fluid,

2. a fluid timing circuit,

3. a variable pressure regulator connected between said control pressuresource and said timing circuit,

4. a main valve connected between said regulator and said timing circuitfor opening and closing a path therebetween,

. a selector valve having a plurality of output ports each connected tothe pilot port of a different one of said coating liquid valves, aninput port selectively connectable to any one of said output ports forselecting said new coating liquid,

6. said timer comprising a plurality of fluid-actuated timing valvesconnected in sequence, each of said valves having a. a first outputport, a second output port, a pilot port,

and an input port normally connected to said first output port andalternatively connectable to said second output port in response tocontrol pressure at said pilot port,

b. a variable restriction valve connected between said timing valveinput port and said pilot port for communicating control pressure tosaid pilot port at some delayed time afier pressure is applied to saidinput port, said delay time being variable by the combined settings ofsaid restriction valve and said regulator,

c. said plurality of timing valves including:

1. first fluid-controlled timing valve having its input portcommunicating with the output port of said main valve, its first outputport communicating with the pilot port of said solvent valve and withthe pilot port of said dump valve, and its second output portcommunicating with the input port of said selector valve forcommunicating control pressure to said pilot ports in accordance withthe positions of said first timing valve and said main valve,

2. a second fluid-controlled timing valve having its input portcommunicating with the second output port of said first valve, its firstoutput port communicating with the pilot port of said dump valve forcommunicating control pressure to said pilot port in accordance with thepositions of said first and second timing valves and said main valve.

2. A pneumatically controlled system according to claim 1 wherein:

said fluid control circuit is a pneumatic control circuit, said sourceof pressurized control fluid being a source of pressurized air, and saidfluid timing circuit being a pneumatic timing circuit.

3. A system according to claim 1 wherein said manifold furthercomprises:

a plurality of double-check valves, one connected in each of the inputports of said manifold, each including a pair of opposed check valves,one of the valves of said pair being said source control valve.

4. A system according to claim 1 wherein said selector valve furthercomprises:

a pneumatically controlled selector lock having a pilot port connectedto the output of said main valve to lock said selector when said valveis open.

5. A system according to claim 1 wherein:

said first timing valve has a time delay of T T, being sufl'rcicntlylong to allow solvent to flow into said manifold but shorter than thetime required for solvent to flow to said gun, for introducing a slug ofsolvent into said line; and

said second timing valve has a time delay of T,, (T plus T,) beingsufficiently long to allow the new coating liquid to flow into saidmanifold to force some of said solvent into said gun passage, butshorter than the time required to force all of said solvent out of saidexhaust line.

6. An automatic quick-change system for replacing an old coating liquidwith a new coating liquid in an apparatus for depositing a coatingliquid on a sub-stratum, said system com prising:

a. a discharge gun having an input port, an exhaust port, a

passage therein communicating with said input and exhaust ports, anonle, a fluid-controlled check valve having a pilot port and connectedbetween said passage and said nozzle for connecting said nozzle to saidpassage in response to control pressure at said check valve pilot P anexhaust line;

c. a fluid-controlled dump valve having a pilot port and connectedbetween said gun exhaust port and said exhaust line for connecting saidgun exhaust port to said exhaust line in response to control pressure atsaid dump valve pilot port;

(1. a manifold having an output port, a solvent input port, an

elongated passage therein communicating with said output port and saidsolvent port, and a plurality of coating liquid input portscommunicating with said manifold passage intermediate said output andsaid solvent input p e. a feed line connected between said manifoldoutput port and said gun input port;

f. a source of pressurized solvent;

g. a fluid-controlled solvent valve having a pilot port and connectedbetween said solvent source and said solvent input port of said manifoldfor connecting said solvent source to said manifold input port inresponse to control pressure at said solvent valve pilot port;

h. a plurality of sources of different pressurized coating liquids;

i. a plurality of fluid-controlled coating liquid valves each having apilot port and each connected to a different one of said coating liquidsources and a different one at said coating liquid input ports of saidmanifold for connecting said one of said sources with said one of saidports in response to control pressure at said coating liquid valve pilotport;

j. a fluid control circuit including:

l a source of pressurized control fluid,

2. a fluid timing circuit,

3. a variable pressure regulator connected between said control pressuresource and said timing circuit,

4. a main valve connected between said regulator and said timing circuitfor opening and closing a path therebetween,

5. a selector valve having a plurality of output ports each connected tothe pilot port of a different one of said coating liquid valves, aninput port selectively connectable to any one of said output ports forselecting said new coating liquid;

6. said timer comprising a plurality of fluid-actuated tim ing valvesconnected in sequence, each of said valves having a. a first outputport, a second output port, a pilot port,

and an input port normally connected to said first output port andalternatively connectable to said second output port in response tocontrol pressure at said pilot port,

b. a variable restriction valve connected between said timing valveinput port and said pilot port for communicating control pressure tosaid pilot port at some delayed time after pressure is applied to saidinput port, said delay time being variable by the combined settings ofsaid restriction valve and said regulator,

c. said plurality of timing valves including:

l. first fluid-controlled timing valve having its input portcommunicating with the output port of said main valve, its first outputport communicating with the pilot port of said solvent valve and withthe pilot port of said dump valve, and its second output portcommunicating with the input port of said selector valve forcommunicating control pressure to said pilot ports in accordance withthe positions of said first timing valve and said main valve,

2. a second fluid-controlled timing valve having its input portcommunicating with the second output port of said first valve, its firstoutput port communicating with the pilot port of said dump valve forcommunicating control pressure to said pilot port in accordance with thepositions of said first and second timing valves and said main valve,

3. a third fluid-controlled valve having its input port communicatingwith the second output port of said second valve and its first outputport communicating with the pilot of the check valve of said gun for forcommunicating pressure to said pilot port in accordance with thepositions of said first, second and third timing valves and said mainvalve, and having a delay time 1",.

7. A pneumatically controlled system according to claim 6 wherein:

said fluid control circuit is a pneumatic control circuit, said sourceof pressurized control fluid being a source of pressurized air, and saidfluid timing circuit being a pneumatic timing circuit.

8. A system according to claim 6 wherein said manifold furthercomprises:

a plurality of double-check valves, one connected in each of the inputports of said manifold, each including a pair of opposed check valves,one of the valves of said pair being said source control valve.

9. A system according to claim 6 wherein said selector valve furthercomprises:

a pneumatically controlled selector lock having a pilot port connectedto the output of said main valve to lock said selector when said valveis open.

10. A system according to claim 6 wherein:

said first timing circuit has a time delay of T,, T, being sufficientlylong to allow solvent to flow into said manifold but shorter than thetime required for solvent to flow to said gun, for introducing a slug ofsolvent into said line,

said second timing circuit has a time delay of T,, (T, plus T,) beingsufficiently long to allow the new coating liquid to flow into saidmanifold to force some of said solvent into said gun passage, butshorter than the time required to force all of said solvent out of saidexhaust line; and

said third timing circuit has a time delay of T '1", being sufficientlylong to purge said old liquid from said nozzle.

1]. A system according to claim 10 wherein T, and T, are in the range offrom 0.1 to 10 seconds and T, is in the range of from 0.! to 3 seconds.

12. A quick-change system for replacing any one liquid from amultiplicity of liquids with a new one of said multiplicity in adischarge apparatus operable to selectively discharge said liquids, saidsystem comprising:

a discharge nozzle;

an exhaust line;

a feed line;

a nozzle control valve for selectively connecting said nozzle to saidfeed line;

an exhaust control valve for selectively connecting said exhaust line tosaid feed line;

a source of liquid solvent;

a solvent control valve for selectively connecting said solvent sourceto said feed line;

a source of each of said multiplicity of liquids;

a multiplicity of liquid control valves for selectively connecting eachof said sources of liquids to said feed line; and

a source of pressurized control fluid;

an all fluid operated control circuit, said circuit including a fluidtiming circuit which is operative upon connection of said source ofpressurized control fluid into said circuit to automatically control thesequencing of said exhaust control valve, said solvent control valve andsaid liquid con trol valves so as to purge said feed line of one liquidby means of solvent flow through said feed line, and to then fill saidfeed line with a second liquid.

13. A quick-change system according to claim 12 wherein:

said fluid control circuit is a pneumatic control circuit and saidsource of pressurized control fluid is a source of pressurized air.

14. A quick-change system according to claim 12 wherein said controlcircuit further comprises:

fluid valve means for selecting said second liquid from saidmultiplicity.

15. A quick-change system according to claim 12 wherein:

said fluid control circuit includes a first control output connected toapply control fluid to said solvent and exhaust control valves to opensaid valves to purge said feed line, and a second control outputconnected to apply control fluid to said exhaust and second liquidcontrol valves to open said valves to fill said feed line.

16. A system according to claim 12 wherein said timing circuit includesfluid means for varying the time of operation thereof.

17. A system according to claim 12 wherein:

said control circuit includes fluid means for operating said nozzlecontrol valve under control of said fluid timing circuit to causesolvent to flow through said nozzle to purge said nozzle.

18. A system according to claim 12 wherein:

said fluid timing circuit comprises a plurality of fluid-actuated timingvalves each of said valves having a. a first output port, a secondoutput port, a pilot port,

and an input port normally connected to said first output port andalternatively connectable to said second output port in response tocontrol pressure at said pilot port,

b. a variable restriction valve connected between said timing valveinput port and said pilot port for communicating control pressure tosaid pilot port at a delayed time after pressure is applied to saidinput port.

19. An automatic, quick-change system for replacing an old liquid with anew liquid in a discharge apparatus for selectively discharging acoating liquid, said system comprising:

a discharge nozzle;

an exhaust line;

a feed line;

a check valve for selectively connecting said nozzle to said feed line;

a dump valve for selectively connecting said exhaust line to said feedline;

a source ofsolvent;

a solvent valve for selectively connecting said solvent source to saidfeed line;

a source of said new liquid;

:1 source valve for selectively connecting said new liquid source tosaid feed line,

controls for operating said dump, solvent, and source valves to causethe presence in said feed line, at some time during a liquid replacingoperation, of said old liquid followed by said new liquid with a slugofsolvent immediately therebetween.

20. The system of claim 19 wherein:

said controls are operable to open said dump and solvent valves for atime T and thereafter to open said dump and new liquid valves for a timeT time T being sufiiciently long to allow solvent to flow into said feedline but shorter than the time required for solvent to flow to saidnozzle, so that a slug of solvent is introduced into said line duringsaid time T and the sum of the times T, and T, being sufficiently longto allow the new liquid to flow into said feed line to force at leastsome of said solvent past said check valve, but shorter than the timerequired to force all of said solvent out of said exhaust line.

21. A system according to claim 19 wherein:

said controls further operate to open said new source and check valvesfor a time T time T, being sufficiently long to allow some of said slugof solvent to pass through said nozzle.

22. A system according to claim 20 wherein:

the time T, is in the range of from 0.5 to 5 seconds, and

the time T is in the range offrom l to 10 seconds.

23. A system according to claim 22 wherein:

said timing circuit opens said check and new source valves for a time T,in the range offrom 0.1 to 1 second.

24. An automatic, quick-change system for replacing an old liquid with anew liquid in a discharge gun for selectively discharging said liquids,said system comprising:

a discharge nozzle;

an exhaust line;

a feed line;

a check valve for selectively connecting said nozzle to said feed line;v a dump valve for selectively connecting said exhaust line to said feedline;

a manifold having an output port, connected to said feed line, a solventinput port, an elongated passage therein communicating with said outputport and said solvent port, and a plurality of liquid input portscommunicating with said manifold passage intermediate said output andsaid solvent input ports;

a plurality of double-check valves, one connected in each of the inputports of said manifold, each including a pair of opposed check valves,one of the valves of said pair being said source control valve;

a pressurized source of solvent;

a solvent valve for selectively connecting said solvent to said solventinput port of said manifold;

a plurality of pressurized sources of liquids;

a plurality of source valves each for selectively connecting a differentone of said liquid sources to a different one of said liquid input portsof said manifold.

t a s s a

1. An automatic quick-change system for replacing an old coating liquidwith a new coating liquid in an apparatus for selectively depositing acoating liquid on a sub-strate, said system comprising: a. a dischargegun having an input port, an exhaust port, a passage thereincommunicating with said input and exhaust ports, a nozzle, a check valveconnected between said passage and said nozzle for connecting saidnozzle to said passage when said check valve is opened; b. an exhaustline; c. a fluid-controlled dump valve having a pilot port and connectedbetween said gun exhaust port and said exhaust line for connecting saidgun exhaust port to said exhaust line in response to control pressure atsaid dump valve pilot port; d. a manifold having an output port, asolvent input port, an elongated passage therein communicating with saidoutput port and said solvent port, and a plurality of coating liquidinput ports communicating with said manifold passage intermediate saidoutput and said solvent input ports; e. a feed line connected betweensaid manifold output port and said gun input port; f. a source ofpressurized solvent; g. a fluid-controlled solvent valve having a pilotport and connected between said solvent source and said solvent inputport of said manifold for connecting said solvent source to saidmanifold input port in response to control pressure at said solventvalve pilot port; h. a plurality of sources of different pressurizedcoating liquids; i. a plurality of fluid-controlled coating liquidvalves each having a pilot port and each connected to a different one ofsaid coating liquid sources and a different one at said one of saidsources with said one of said ports in response to control pressure atsaid coating liquid valve pilot port; j. a fluid control circuitincluding:
 1. a source of pressurized control fluid,
 2. a fluid timingcircuit,
 3. a variable pressure regulator connected between said controlpressure source and said timing circuit,
 4. a main valve connectedbetween said regulator and said timing circuit for opening and closing apath therebetween,
 5. a selector valve having a plurality of outputports each connected to the pilot port of a different one of saidcoating liquid valves, an input port selectively connectable to any oneof said output ports for selecting said new coating liquid,
 6. saidtimer comprising a plurality of fluid-actuated timing valves connectedin sequence, each of said valves having a. a first output port, a secondoutput port, a pilot port, and an input port normally connected to saidfirst output port and alternatively connectable to said second outputport in response to control pressure at said pilot port, b. a variablerestriction valve connected between said timing valve input port andsaid pilot Port for communicating control pressure to said pilot port atsome delayed time after pressure is applied to said input port, saiddelay time being variable by the combined settings of said restrictionvalve and said regulator, c. said plurality of timing valvesincluding:
 1. first fluid-controlled timing valve having its input portcommunicating with the output port of said main valve, its first outputport communicating with the pilot port of said solvent valve and withthe pilot port of said dump valve, and its second output portcommunicating with the input port of said selector valve forcommunicating control pressure to said pilot ports in accordance withthe positions of said first timing valve and said main valve,
 2. asecond fluid-controlled timing valve having its input port communicatingwith the second output port of said first valve, its first output portcommunicating with the pilot port of said dump valve for communicatingcontrol pressure to said pilot port in accordance with the positions ofsaid first and second timing valves and said main valve.
 2. a fluidtiming circuit,
 2. a second fluid-controlled timing valve having itsinput port communicating with the second output port of said firstvalve, its first output port communicating with the pilot port of saiddump valve for communicating control pressure to said pilot port inaccordance with the positions of said first and second timing valves andsaid main valve.
 2. A pneumatically controlled system according to claim1 wherein: said fluid control circuit is a pneumatic control circuit,said source of pressurized control fluid being a source of pressurizedair, and said fluid timing circuit being a pneumatic timing circuit. 2.a fluid timing circuit,
 2. a second fluid-controlled timing valve havingits input port communicating with the second output port of said firstvalve, its first output port communicating with the pilot port of saiddump valve for communicating control pressure to said pilot port inaccordance with the positions of said first and second timing valves andsaid main valve,
 3. a third fluid-controlled valve having its input portcommunicating with the second output port of said second valve and itsfirst output port communicating with the pilot of the check valve ofsaid gun for for communicating pressure to said pilot port in accordancewith the positions of said first, second and third timing valves andsaid main valve, and having a delay time T3.
 3. a variable pressureregulator connected between said control pressure source and said timingcircuit,
 3. A system according to claim 1 wherein said manifold furthercomprises: a plurality of double-check valves, one connected in each ofthe input ports of said manifold, each including a pair of opposed checkvalves, one of the valves of said pair being said source control valve.3. a variable pressure regulator connected between said control pressuresource and said timing circuit,
 4. a main valve connected between saidregulator and said timing circuit for opening and closing a paththerebetween,
 4. A system according to claim 1 wherein said selectorvalve further comprises: a pneumatically controlled selector lock havinga pilot port connected to the output of said main valve to lock saidselector when said valve is open.
 4. a main valve connected between saidregulator and said timing circuit for opening and closing a paththerebetween,
 5. a selector valve having a plurality of output portseach connected to the pilot port of a different one of said coatingliquid valves, an input port selectively connectable to any one of saidoutput ports for selecting said new coating liquid;
 5. A systemaccording to claim 1 wherein: said first timing valve has a time delayof T1, T1 being sufficiently long to allow solvent to flow into saidmanifold but shorter than the time required for solvent to flow to saidgun, for introducing a slug of solvent into said line; and said secondtiming valve has a time delay of T2, (T1 plus T2) being sufficientlylong to allow the new coating liquid to flow into said manifold to forcesome of said solvent into said gun passage, but shorter than the timerequired to force all of said solvent out of said exhaust line.
 5. aselector valve having a plurality of output ports each connected to thepilot port of a different one of said coating liquid valves, an inputport selectively connectable to any one of said output ports forselecting said new coating liquid,
 6. said timer comprising a pluralityof fluid-actuated timing valves connected in sequence, each of saidvalves having a. a first output port, a second output port, a pilotport, and an input port normally connected to said first output port andalternatively connectable to said second output port in response tocontrol pressure at said pilot port, b. a variable restriction valveconnected between said timing valve input port and said pilot Port forcommunicating control pressure to said pilot port at some delayed timeafter pressure is applied to said input port, said delay time beingvariable by the combined settings of said restriction valve and saidregulator, c. said plurality of timing valves including:
 6. An automaticquick-change system for replacing an old coating liquid with a newcoating liquid in an apparatus for depositing a coating liquid on asub-stratum, said system comprising: a. a discharge gun having an inputport, an exhaust port, a passage therein communicating with said inputand exhaust ports, a nozzle, a fluid-controlled check valve having apilot port and connected between said passage and said nozzle forconnecting said nozzle to said passage in response to control pressureat said check valve pilot port; b. an exhaust line; c. afluid-controlled dump valve having a pilot port and connected betweensaid gun exhaust port and said exhaust line for connecting said gunexhaust port to said exhaust line in response to control pressure atsaid dump valve pilot port; d. a manifold having an output port, asolvent input port, an elongated passage therein communicating with saidoutput port and said solvent port, and a plurality of coating liquidinput ports communicating with said manifold passage intermediate saidoutput and said solvent input ports; e. a feed line connected betweensaid manifold output port and said gun input port; f. a source ofpressurized solvent; g. a fluid-controlled solvent valve having a pilotport and connected between said solvent source and said solvent inputport of said manifold for connecting said solvent source to saidmanifold input port in response to control pressure at said solventvalve pilot porT; h. a plurality of sources of different pressurizedcoating liquids; i. a plurality of fluid-controlled coating liquidvalves each having a pilot port and each connected to a different one ofsaid coating liquid sources and a different one at said coating liquidinput ports of said manifold for connecting said one of said sourceswith said one of said ports in response to control pressure at saidcoating liquid valve pilot port; j. a fluid control circuit including:6. said timer comprising a plurality of fluid-actuated timing valvesconnected in sequence, each of said valves having a. a first outputport, a second output port, a pilot port, and an input port normallyconnected to said first output port and alternatively connectable tosaid second output port in response to control pressure at said pilotport, b. a variable restriction valve connected between said timingvalve input port and said pilot port for communicating control pressureto said pilot port at some delayed time after pressure is applied tosaid input port, said delay time being variable by the combined settingsof said restriction valve and said regulator, c. said plurality oftiming valves including:
 7. A pneumatically controlled system accordingto claim 6 wherein: said fluid control circuit is a pneumatic controlcircuit, said source of pressurized control fluid being a source ofpressurized air, and said fluid timing circuit being a pneumatic timingcircuit.
 8. A system according to claim 6 wherein said manifold furthercomprises: a plurality of double-check valves, one connected in each ofthe input ports of said manifold, each including a pair of opposed checkvalves, one of the valves of said pair being said source control valve.9. A system according to claim 6 wherein said selector valve furthercomprises: a pneumatically controlled selector lock having a pilot portconnected to the output of said main valve to lock said selector whensaid valve is open.
 10. A system according to claim 6 wherein: saidfirst timing circuit has a time delay of T1, T1 being sufficiently longto allow solvent to flow into said manifold but shorter tHan the timerequired for solvent to flow to said gun, for introducing a slug ofsolvent into said line, said second timing circuit has a time delay ofT2, (T1 plus T2) being sufficiently long to allow the new coating liquidto flow into said manifold to force some of said solvent into said gunpassage, but shorter than the time required to force all of said solventout of said exhaust line; and said third timing circuit has a time delayof T3, T3 being sufficiently long to purge said old liquid from saidnozzle.
 11. A system according to claim 10 wherein T1 and T2 are in therange of from 0.1 to 10 seconds and T3 is in the range of from 0.1 to 3seconds.
 12. A quick-change system for replacing any one liquid from amultiplicity of liquids with a new one of said multiplicity in adischarge apparatus operable to selectively discharge said liquids, saidsystem comprising: a discharge nozzle; an exhaust line; a feed line; anozzle control valve for selectively connecting said nozzle to said feedline; an exhaust control valve for selectively connecting said exhaustline to said feed line; a source of liquid solvent; a solvent controlvalve for selectively connecting said solvent source to said feed line;a source of each of said multiplicity of liquids; a multiplicity ofliquid control valves for selectively connecting each of said sources ofliquids to said feed line; and a source of pressurized control fluid; anall fluid operated control circuit, said circuit including a fluidtiming circuit which is operative upon connection of said source ofpressurized control fluid into said circuit to automatically control thesequencing of said exhaust control valve, said solvent control valve andsaid liquid control valves so as to purge said feed line of one liquidby means of solvent flow through said feed line, and to then fill saidfeed line with a second liquid.
 13. A quick-change system according toclaim 12 wherein: said fluid control circuit is a pneumatic controlcircuit and said source of pressurized control fluid is a source ofpressurized air.
 14. A quick-change system according to claim 12 whereinsaid control circuit further comprises: fluid valve means for selectingsaid second liquid from said multiplicity.
 15. A quick-change systemaccording to claim 12 wherein: said fluid control circuit includes afirst control output connected to apply control fluid to said solventand exhaust control valves to open said valves to purge said feed line,and a second control output connected to apply control fluid to saidexhaust and second liquid control valves to open said valves to fillsaid feed line.
 16. A system according to claim 12 wherein said timingcircuit includes fluid means for varying the time of operation thereof.17. A system according to claim 12 wherein: said control circuitincludes fluid means for operating said nozzle control valve undercontrol of said fluid timing circuit to cause solvent to flow throughsaid nozzle to purge said nozzle.
 18. A system according to claim 12wherein: said fluid timing circuit comprises a plurality offluid-actuated timing valves each of said valves having a. a firstoutput port, a second output port, a pilot port, and an input portnormally connected to said first output port and alternativelyconnectable to said second output port in response to control pressureat said pilot port, b. a variable restriction valve connected betweensaid timing valve input port and said pilot port for communicatingcontrol pressure to said pilot port at a delayed time after pressure isapplied to said input port.
 19. An automatic, quick-change system forreplacing an old liquid with a new liquid in a discharge apparatus forselectively discharging a coating liquid, said system comprising: adischarge nozzle; an exhaUst line; a feed line; a check valve forselectively connecting said nozzle to said feed line; a dump valve forselectively connecting said exhaust line to said feed line; a source ofsolvent; a solvent valve for selectively connecting said solvent sourceto said feed line; a source of said new liquid; a source valve forselectively connecting said new liquid source to said feed line;controls for operating said dump, solvent, and source valves to causethe presence in said feed line, at some time during a liquid replacingoperation, of said old liquid followed by said new liquid with a slug ofsolvent immediately therebetween.
 20. The system of claim 19 wherein:said controls are operable to open said dump and solvent valves for atime T1 and thereafter to open said dump and new liquid valves for atime T2; time T1 being sufficiently long to allow solvent to flow intosaid feed line but shorter than the time required for solvent to flow tosaid nozzle, so that a slug of solvent is introduced into said lineduring said time T1; and the sum of the times T1 and T2 beingsufficiently long to allow the new liquid to flow into said feed line toforce at least some of said solvent past said check valve, but shorterthan the time required to force all of said solvent out of said exhaustline.
 21. A system according to claim 19 wherein: said controls furtheroperate to open said new source and check valves for a time T3, time T3being sufficiently long to allow some of said slug of solvent to passthrough said nozzle.
 22. A system according to claim 20 wherein: thetime T1 is in the range of from 0.5 to 5 seconds, and the time T2 is inthe range of from 1 to 10 seconds.
 23. A system according to claim 22wherein: said timing circuit opens said check and new source valves fora time T3 in the range of from 0.1 to 1 second.
 24. An automatic,quick-change system for replacing an old liquid with a new liquid in adischarge gun for selectively discharging said liquids, said systemcomprising: a discharge nozzle; an exhaust line; a feed line; a checkvalve for selectively connecting said nozzle to said feed line; a dumpvalve for selectively connecting said exhaust line to said feed line; amanifold having an output port, connected to said feed line, a solventinput port, an elongated passage therein communicating with said outputport and said solvent port, and a plurality of liquid input portscommunicating with said manifold passage intermediate said output andsaid solvent input ports; a plurality of double-check valves, oneconnected in each of the input ports of said manifold, each including apair of opposed check valves, one of the valves of said pair being saidsource control valve; a pressurized source of solvent; a solvent valvefor selectively connecting said solvent to said solvent input port ofsaid manifold; a plurality of pressurized sources of liquids; aplurality of source valves each for selectively connecting a differentone of said liquid sources to a different one of said liquid input portsof said manifold.